Begin by making the custard. In a 3-quart (2.8-liter) saucepan over medium heat, warm the heavy whipping cream, whole milk, and light brown sugar until the sugar dissolves, about 3 minutes. Remove from the heat.
1 cup (240 ml) heavy whipping cream, 1 cup (240 ml) whole milk, ¼ cup (60 g) packed light brown sugar
In a mixing bowl, whisk the egg yolks until light yellow. Add the granulated sugar and whisk until blended.
6 large egg yolks, ¼ cup (50 g) granulated sugar
Slowly whisk one-fourth of the warm cream mixture into the egg mixture to temper the yolks. Add it gradually to prevent scrambling. Continue whisking while slowly adding the remaining cream mixture. Whisk in the pumpkin purée, chai tea concentrate, orange zest, and vanilla extract until smooth. If there is any hint of cooked egg, strain the custard through a fine mesh sieve and add the orange zest after straining instead of before.
½ cup (120 g) pumpkin purée , ⅓ cup (80 ml) chai concentrate, 2 tsps (2 g) orange zest, 1 tsp (5 ml) vanilla extract
Divide the custard among six 6-ounce (175 ml) ramekins. Set the ramekins in a 12 × 16-inch (30 × 40 cm) roasting pan at least 2 inches (5 cm) deep. Place the pan in the oven and pour in boiling water until it reaches halfway up the sides of the ramekins.
Bake at 325°F (165°C) until the custards barely jiggle when gently shaken, 45 to 50 minutes. Lift the ramekins out of the water bath and cool on a rack for 30 minutes. Chill until completely cold, 4 to 6 hours. Cover once cold.
To make the brittle, melt the granulated sugar and water in a small nonstick frying pan (6 to 8 inches, 15 to 20 cm) over medium-high heat, stirring until the sugar dissolves, 1 to 2 minutes. Cook without stirring, shaking the pan often, until the mixture reaches a deep amber color, 5 to 10 minutes.
⅓ cup (67 g) granulated sugar, ¼ cup (60 ml) water
Remove from the heat and stir in the pepitas. Immediately pour the mixture onto buttered parchment or foil and spread thin with a spatula.
½ cup (70 g) pepitas (pumpkin) seeds, butter
Let the brittle cool until firm, about 10 minutes. Break into shards for serving. Store airtight if not using immediately.